<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        const xhr=new XMLHttpRequest()
        xhr.open('GET','http://localhost:3000')
        xhr.send()
        xhr.onreadystatechange=function(){
            if(xhr.readyState===4){//0---请求准备中,1---请求已发送,2---请求已接收,3---请求处理中,4---请求已完成
                if(xhr.status===200){
                    console.log(xhr.responseText)
                }
            }
        }


    </script>
</body>
</html>